Detailed Description of the Invention
This invention relates to an air-fuel ratio feedback control system for controlling the air-fuel ratio of an air-fuel mixture to be supplied to an internal combustion engine by sensing and feeding back the oxygen concentration of engine exhaust gases which is representative of the air-fuel ratio of the supplied air-fuel mixture.
In order to purify exhaust gases from an internal combustion engine, it has heretofore been proposed to sense and feed back the oxygen concentration of exhaust gases in order to control the air-fuel ratio of an air-fuel mixture in accordance with the oxygen concentration so that the ratio is equal to, for example, a constant theoretical air-fuel ratio. This method of feedback control has proved to be advantageous in that the air-fuel ratio remains constant even though major changes occur in outside environments such as atmospheric pressure variations, intake air temperature changes and so forth. Further, it has been verified that with the integration of inverted oxygen concentration measurements in a feedback control loop, control speed is improved. However, if this feedback control is made operative during all engine operating conditions, a problem arises that desired power demands are not met at acceleration and full loads, since the air-fuel ratio is held at a constant level. Further, this feedback control method has the disadvantage that it fails to provide lean fuel mixtures during deceleration or no loads.